Cable terminating device



May 8, 1951 A. D. FERGUSON 2,552,162

CABLE TERMINATING DEVICE Filed Jan'. 19, 1946 Inventor: Alexander D. Ferguson has/M 29M H is Attorn ey.

Patented May 8, 1951 CABLE TERMINATING DEVICE Alexander D. Ferguson, Sale, England, assignor, by mesne assignments, to General Electric Company, a corporation of New York Application January 19, 1946, Serial No. 642,266 In England November 26, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires November 26, 1961 2 Claims. 1

My invention relates to devices for terminating electrical cables and it has for its primary object to provide an improved terminating device in which one or more conductive members are enclosed in a moisture-tight manner in a cable head of insulating material.

In the construction of an antenna of the dipole type for short wave radio transmission or reception, it is customary to employ a cable of the coaxial line type for connecting radio apparatus to the antenna. In such a structure, it is most desirable that connection of the antenna with the sheathing of the cable be made moisture-tight and also be so constructed that the antenna is located and maintained in comparatively accurate positioning with respect to the cable. It is another object of my invention to provide a new and improved method for forming a moisture-tight cable terminating device.

One of the features of my invention is the provision of a cable terminating device which is produced by locating an electrically conducting member or members and the connecting cable end in place within a mold by means of one or more registering members registering with the inner surface of the mold and injecting under pressure into said mold a mass of a resinous material, such as polyethylene, thereby to embed the conductive member or members in the mass. The registering members are likewise formed of suitable dielectric materials and are provided with interfaces adapted to prevent the entrance of moisture through the interfaces into the device.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself may best be understood by reference to the following description taken in connection with the accompanying drawing the single figure of which is a sectional elevation of the cable terminating device of my invention within a mold used in its construction.

The cable terminating device is a radiating element or antenna of the dipole type comprising a pair of conducting members I and 2 which extend in line with one another perpendicularly to the cable, the end of which appears at 3, and in opposite directions from said cable.

The cable comprises a central core member 4 surrounded by a concentric tubular conductor 5 and insulated therefrom by a'suitable dielectric material 6, such as polyethylene. This tubular conductor is itself surrounded by an outer metallic conductor 1 of suitable form, for example a brass tube, which is insulated from the tubular conducing operation. At their outer ends, the rods are received in closed bores in respective caps IE3 and II These caps maybe formed of any suit,- able insulating material, such as pure or plasticized polyethylene in any combination. In order to provide a desirable interlocking action between the interfaces of the caps and the main mass of polyethylene, the caps II), II may have an external surface containing a plurality of rectangular grooves I2.

In the manufacture of the cable terminating device, the cable end 3 and the rods I and 2, after insertion in the bores of the caps II), M, are located within a mold I3. The mold I3 comprises an upper wall I4 and a lower wall I5 and is provided with a cylindrical end portion I6 in which the larger portions of the caps I9 and II are received and are located in position, thereby accurately to determine the position of the outer ends of the rods I and 2 in the mold. The rods are located along the axial direction thereof by abutment of the caps against removable end walls I! of the mold. The end walls may be secured'to the members I 4, I5 by means of a plurality of fastening devices, such as the cap screws It.

Means are provided for securing the molded plastic material to the outermost conductor of the cable and comprise a plurality of grooves I9 which may be of rectangular, or preferably of undercut, cross section and which are formed on the outer surface of the conductor 7. The mold I3 is likewise provided with a cylindrical annex 2B in which is located the portion of the cable on which the grooves I9 are formed. The polyethylene is injected into the mold, such as through an orifice 2|, and flows into the cylindrical portions Iii of the mold so as to effect an interlocking relation between the main mass 22 and the peripheral grooves I2. The polyethylene flows also into the annex 20 so as to efiect a moisture-tight connection with the end of the conductor I of the cable.

Polyethylene, the plastic material which I have indicated as suitable for use in my improved terminating device, is a polymer of ethylene which has suitable electrical and other properties for use inter alia with very high frequencies and which, while being moldable at a temperature low enough not to injure the insulation of the cable, does not sufi'er from the disadvantage of having too low a softening temperature or being liable to deformation by flow at ordinary atmospheric temperatures, so that the desired accurate positioning of the conductive members is retained. Alternatively, instead of polyethylene being used for the main mass referred to and for the caps I0, I I, the mass and members may be formed of plasticized polystyrene.

In producing the cable terminating device according to the invention, the mold i3 is generally heated to a temperature which is considerably below that at which the polyethylene or plasticized polystyrene is injected and while the injected material is arranged to interlock with the caps In, II it is not necessary that difiusion between the injected material and the caps at the interfaces thereof shall occur.

It is to be understood that the terminating device may include one or more other conductive members, such as parasitic directors, which are also located in place by caps or registering members of polyethylene, which are received in suitable portions of the mold, and which may not be connected with a conductor of the cable. For example, as shown in the drawing, there may be arranged parallel with the rods I and 2 a further rod 23 which extends across the terminating device and which is received at its ends in closed bores in two further end caps 24, 25 registered in further cylindrical end portions 26 of the mold.

Conveniently, the mold is split in a cross-sectional plane diametrically of the cable, as shown at 27 in the drawing, and is fastened together by means of a plurality of bolts 28. In such case, the cross section of the main mass 22 of the insulating material may be oval over a central portion thereof, while the rods I, 2, 23 are located in respective arms of a circular cross section determined, in part, by the dividing portions 29 of the mold.

The polyethylene 6 located between the conductors 4 and is preferably undercut so as to have a shoulder 30 disposed below the end of the conductor 5 whereby, during the injection, part of the main mass 22 of polyethylene on passing into the mold flows into the space between the reduced diameter end of the original polyethylene 6 and the conductor 5. Such construction provides, on the one hand, a lengthened interface between the plastic material originally in the cable and that injected into the mold during the formation of the terminating device and, on the other hand, a hermetic seal between the two masses of plastic material by reason of thermal contraction of the injected material on to the cooler original material 6. In this way, the desired value of breakdown voltage is maintained between the innermost conductor and the adjacent conductor.

An important advantage of the structure of my improved terminating device is that, as a result of the fairly large coefiicient of thermal expansion possessed by polyethylene, the shrinkage of the injected polyethylene on the various members effects a moisture-tight seal. At the same time, the provision of interfaces provides interlocking between the component parts and the 4 injected mass so that the conductive members are maintained in comparatively accurate positioning within the mass of insulating material.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention in its broader aspects and I therefore aim in the appended claims to cover all changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A terminating device for a coaxial cable of the type comprising a tubular outer conductor and a centraly disposed inner conductor comprising a. pair of conductive members connected respectively to corresponding ends of said conductors and extending in a direction transverse to said conductors, an additional conductor parallel with said members and having a length substantially equal to the combined lengths of said members, said additional member being located on the sides of said members remote from said conductors, caps surrounding respectively the ends of said additional member and the ends of said respective members remote from said conductors, and a mass of plastic material surrounding at least a portion of each of said caps, said additional member, said conductive members, and the ends of said conductors.

2. In combination, a cable comprising a tubular outer conductor and a centrally disposed inner conductor, a conductive sleeve surrounding said outer conductor and spaced therefrom, solid insulating means disposed between said conductors and between said outer conductor and said sleeve, respective conductive members connected to said conductors at the ends thereof and disposed in a direction substantially transverse to said conductors, each of said conductive members having a cap member enclosing its ends remote from said conductors, and a mass of plastic material surrounding the ends of said conductors, said conductive members, and the end of said sleeve, said caps having a surface shaped to interlock with said mass, and said outer sleeve having a groove adapted to interlock with said mass.

ALEXANDER D. FERGUSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,069,820 Sessions Aug. 12, 1913 1,333,004 Vaugh Mar. 9, 1920 1,745,342 Yagi Jan. 28, 1930 1,837,142 Bailey Dec. 15, 1931 1,934,412 Englund Nov. 7, 1933 2,063,641 Billiard Dec. 8, 1936 2,161,292 I-Iahnemann June 6, 1939 2,193,017 Bassett Mar. 12, 1940 2,213,276 Gossel Sept. 3, 1940 2,370,053 Lindenblad Feb. 20, 1945 

